Anal. Chem. 2004, 76, 2544-2552
Ultraflat Carbon Film Electrodes Prepared by Electron Beam Evaporation Jason J. Blackstock,† Abbas A. Rostami,‡,§ Aletha M. Nowak,| Richard L. McCreery,| Mark R. Freeman,† and Mark T. McDermott*,‡
Department of Physics and Department of Chemistry, University of Alberta, Edmonton, Canada, T6G2J1, and Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
A facile method for the preparation of thin-film carbon electrodes by electron beam evaporation onto highly doped silicon is presented. The physical and electrochemical properties of these films both before and after postdeposition pyrolysis are investigated. Raman spectroscopy establishes the amorphous structure of the nonpyrolyzed carbon films and confirms the formation of graphitic carbon after pyrolysis at 1000 °C. Scanning force microscopy reveals the root-mean-square roughness of nonpyrolyzed films to be ∼1 Å, while pyrolyzed films exhibit an increased roughness of ∼4 Å. The electrochemical behavior of the electrodes resembles glassy carbon, with measured heterogeneous electron-transfer rate constants among the highest measured for thin carbon films. These carbon film electrodes will potentially find applications in such fields as molecular electronics and scanning probe microscopy of adsorbed species. Due to a number of advantageous properties, carbon materials have been commonly employed in electroanalysis, electrocatalysis, and electrosynthesis.1-3 In recent years, attention has been drawn to the fabrication of low-cost, disposable, carbon film electrodes for mass-scale use as electrochemical sensors.4-7 Relatively thick films are commonly prepared by printing from commercial carbon ink.5,8-10 These types of films often yield widely varying electrochemical reactivity due to binding polymers and other adhesion * To whom correspondence should be addressed. Voice: 780-492-3687. Fax: 780-492-8231. E-mail:
[email protected]. † Department of Physics, University of Alberta. ‡ Department of Chemistry, University of Alberta. § On leave from the University of Mazandaran, Iran. | The Ohio State University. (1) Kinoshita, K. Carbon: Electrochemical and Physicochemical Properties; Wiley: New York, 1988. (2) McCreery, R. L. In Electroanalytical Chemistry; Bard, A. J., Ed.; Marcel Dekker: New York, 1991; Vol. 17, pp 221-374. (3) McCreery, R. L. In Interfacial Electrochemistry; Wiekowski, A., Ed.; Dekker: New York, 1999; Chapter 35. (4) Alvarez-Icaza, M.; Bilitewski, U. Anal. Chem. 1993, 65, 525A. (5) Hart, J. P.; Wring, S. A. Electroanalysis 1994, 6, 617-624. (6) Lindner, E.; Buck, R. P. Anal. Chem. 2000, 72, 336A-345A. (7) Wang, J.; Tian, B. M.; Nascimento, V. B.; Angnes, L. Electrochim. Acta 1998, 43, 3459-3465. (8) Wang, J.; Pamidi, P. V. A.; Park, D. S. Anal. Chem. 1996, 68, 2705-2708. (9) Wang, J.; Pedrero, M.; Pamidi, P. V. A.; Cai, X. H. Electroanalysis 1995, 7, 1032-1034. (10) Wang, J.; Pedrero, M.; Sakslund, H.; Hammerich, O.; Pingarron, J. Analyst 1996, 121, 345-350.
2544 Analytical Chemistry, Vol. 76, No. 9, May 1, 2004
promoters present in the variety of carbon inks used.7 Several methods have been reported for the fabrication of thin-film (e400 nm) electrodes including chemical vapor deposition (CVD) of carbon containing gases,11,12 sputtering,13-16 electron-beam (ebeam) evaporation17,18 and the pyrolysis of polymeric thin films.19-23 In general, these thin film carbon electrodes are highly pure, contain some graphitic microstructure, are easily mass-produced, and yield electrochemical reactivity comparable to glassy carbon (GC). Another characteristic of some carbon thin films that is proving useful for modern applications is surface flatness. Recently, the electrochemical reactivity of pyrolyzed photoresist film (PPF) electrodes, with an root-mean-square (rms) roughness of
